High deflection hydrofoils and swim fins

Abstract

Designs and methods are disclosed for permitting permit scooped shaped swim fin blades ( 184 ) to flex around a transverse axis to a significantly reduced angle of attack while reducing or preventing the scooped blade portion ( 254 ) from collapsing or buckling under the longitudinal compression forces ( 222 ) exerted on the scooped portion during a large scale blade deflection ( 212 ) by strategically alleviating or controlling such compression forces ( 222 ). Method are also disclosed for increasing flow capacity, effective scoop length, scoop depth over a greater length of the blade, reducing blade resistance to large scale deflections, reducing bending resistance within scooped blade portions ( 254 ) that are experiencing high levels of blade deflection. Methods are also provided for reducing lost motion and increasing propulsion during the inversion phase of a reciprocating kicking stroke cycle while also increasing the formation of a scooped blade region ( 254 ) during the inversion phase of the stroke cycle.

1 - 20 . (canceled)  
     
     
         21 . A method for providing a propulsion hydrofoil, comprising: 
 (a) providing said hydrofoil with a blade member connected to a predetermined body, said blade member having an attacking surface, a lee surface, outer side edges, a root portion near said predetermined body and a free end portion spaced from said predetermined body, said blade member having a predetermined length between said root portion and said free end portion, said blade member having a longitudinal midpoint between said root portion and said free end portion, said blade member having a first half blade portion between said root portion and said longitudinal midpoint and a second half portion between said longitudinal midpoint and said free end portion, said blade member having sufficient flexibility to bow between said outer side edges to form a longitudinal channel shaped contour, said longitudinal channel shaped contour extends from said free end portion toward said root portion to base of said longitudinal channel shaped contour, said base being located a predetermined distance from said predetermined body, said longitudinal channel shaped contour having a predetermined longitudinal dimension between said free end portion and said base;    (b) providing said blade member with two longitudinal stiffening members connected to said outer side edges, said longitudinal stiffening members having an upper surface notch having a predetermined upper surface longitudinal dimension and lower surface notch having a predetermined lower surface longitudinal dimension, said predetermined upper surface longitudinal dimension being different than said predetermined lower surface longitudinal dimension, said upper surface notch and said lower surface notch being disposed within said first half blade portion of said blade member and are arranged to provide said blade member with sufficient flexibility to experience a predetermined lengthwise deflection from a predetermined neutral orientation to a predetermined reduced lengthwise angle of attach around a transverse axis during use, said transverse axis being located within said first half portion of said blade member; and    (c) providing said blade member with sufficient spring-like tension during said predetermined lengthwise deflection so as to permit said blade member to experience a significantly strong snapping motion from said predetermined lengthwise deflection toward said predetermined neutral position.